PostgreSQL is a relational database management system that uses a client-server architecture, where the server processes and shared memory work together to build an instance that handles data access. The instance controls fragmentation, which allows for controlling where data is stored at the table level according to some algorithm or scheme. Fragmentation can lead to bloating, where deleted data remains in the table but its space is not released, causing performance degradation over time. To mitigate this, PostgreSQL requires periodic VACUUM operations to free up unutilized space and defragment tables. In contrast, SingleStoreDB automatically optimizes tables, supports online optimization, and has background threads that optimize columnstore indexes as needed, allowing for fast ingestion, high query speed, and a robust, scalable solution.